Update and Improve Subsection NH –– Alternative Simplified Creep-Fatigue Design Methods
This report described the results of investigation on Task 10 of DOE/ASME Materials NGNP/Generation IV Project based on a contract between ASME Standards Technology, LLC (ASME ST-LLC) and Japan Atomic Energy Agency (JAEA). Task 10 is to Update and Improve Subsection NH -- Alternative Simplified Creep-Fatigue Design Methods. Five newly proposed promising creep-fatigue evaluation methods were investigated. Those are (1) modified ductility exhaustion method, (2) strain range separation method, (3) approach for pressure vessel application, (4) hybrid method of time fraction and ductility exhaustion, and (5) simplified model test approach. The outlines of those methods are presented first, and predictability of experimental results of these methods is demonstrated using the creep-fatigue data collected in previous Tasks 3 and 5. All the methods (except the simplified model test approach which is not ready for application) predicted experimental results fairly accurately. On the other hand, predicted creep-fatigue life in long-term regions showed considerable differences among the methodologies. These differences come from the concepts each method is based on. All the new methods investigated in this report have advantages over the currently employed time fraction rule and offer technical insights that should be thought much of in the improvement of creep-fatigue evaluation procedures. The main points of the modified ductility exhaustion method, the strain range separation method, the approach for pressure vessel application and the hybrid method can be reflected in the improvement of the current time fraction rule. The simplified mode test approach would offer a whole new advantage including robustness and simplicity which are definitely attractive but this approach is yet to be validated for implementation at this point. Therefore, this report recommends the following two steps as a course of improvement of NH based on newly proposed creep-fatigue evaluation methodologies. The first step is to modify the current approach by incorporating the partial advantages the new method offer, and the second step is to replace the current method by the simplified test approach when it has become technically mature enough. The recommendations are basically in line with the work scope of the Task Force on Creep-Fatigue of the Subgroup on Elevated Temperature Design of the Standards Committee of the ASME Boiler and Pressure Vessel Committee Section III.
- Research Organization:
- ASME Standards Technology, LLC.
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- FC07-05ID14712
- OSTI ID:
- 974288
- Report Number(s):
- DOE/ID14712-10; TRN: US1003092
- Country of Publication:
- United States
- Language:
- English
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